1. Field of the Invention
The present invention relates to a method and apparatus to control and limit the emission and discharge of volatile and malodorous contaminants, such as those identified as VCs, VOCs, VICs, NOx, SOx, MCs, HAPs and other regulated contaminants,
2. Description of Prior Art
Numerous compounds used in various industries are recognized as environmental health hazards and pollutants. Regulatory control in the United States and other countries has led to constantly increasing restrictions on discharge of such contaminants. While various separation and destruction methods have been utilized to remove contaminants from those waste products requiring disposal, many of the methods utilized are prohibitively expensive, especially for small facilities with limited resources. Low concentration high volume flows carry large energy and power penalties when treated with conventional technologies, and contribute to green house gas problems. Many small emission sources remain uncontrolled due to the prohibitive cost of installing and operating conventional systems.
Air contaminants are produced by many industries in many forms. Some industries produce Volatile Contaminants (VCs), Hazardous Air Pollutants (HAPs), or Malodorous Compounds (MCs) as part of a waste gas stream. Many industrial processes are dependent on evaporative processes that contaminate fluid process flows with VCs, HAPs, or MCs. In other industries, the contaminants are absorbed into a liquid solvent making the solvent unfit for further use. Contaminants may be entrained as a result of a scrubber process, or as a result of a processing of other materials. These contaminants can be present in liquid or gas streams depending on the industry or the source. VOCs are also found in contaminated ground water and soil. Such occurrences lead to the need for remediation.
Regulations on air quality affect a wide variety of industries. The Federal Clean Air Act (FCAA) applies to air emissions establishing air quality standards, emission standards for hazardous air pollutants, new source performance standards, acid deposition limits, and particulate discharge emission limits. The Federal Clean Water Act (FCWA) addresses control of pollutants to the environment through liquid discharge. Hydrocarbon and petrochemical industries are affected by these restrictions. Industries that burn fossil fuels, such as for power generation, are also affected by these emission limits. From paint shops and bakeries to dry cleaners, there is a need for a method and apparatus to dispose or destroy these contaminants. Such treatment methods must operate in an efficient and cost-effective manner without producing new pollutants or depleting valuable resources.
One of the methods currently available for handling contaminants is equilibrium distillation. To achieve high purity products requires an increased number of stages, increased energy input to increase reflux and/or vessels designed for non-atmospheric pressure operation. When multiple solvents are combined prior to being regenerated, close relative volatilities and azeotropes can make equilibrium separation particularly difficult. While solvent can be recovered by this method, some solvent is typically lost to the contaminant by-product. Furthermore, while the major portion of contaminants may be concentrated in one by-product, the contaminant remains essentially in the same form and thus requires further treatment to complete disposal or destruction of the contaminant. These methods simply concentrate the contaminants that must then go to disposal or further treatment and separation steps.
Numerous filtration methods have also been utilized including ultrafiltration techniques. Various entrained solids or filter aids have been tried including activated carbons, titanium oxides, aluminas, iron oxides and silicas. Filter media with contaminants then face the same disposal challenge since the contaminants are trapped within the media.
Destruction techniques involve subjecting the contaminants to extreme thermal conditions such that the contaminants are broken down into simpler components, such as CO2, H2O and even elemental components. Destruction techniques typically involve large additional energy inputs and substantial space requirements. This combination is often economically inefficient for significant volumes of throughput and wastes limited hydrocarbon resources. Available destruction techniques include thermal oxidation, incineration, and catalytic incineration/oxidation. Incineration, i.e., oxidative destruction, seeks to oxidize the contaminants to produce primarily CO2 and H2O. Notably, the release of CO2 is also becoming regulated as a greenhouse gas and may soon have limits placed on its discharge. Particulate matter tends to negatively affect some incineration processes as well as release particulate matter that contributes to ground level ozone (smog) formation.
Thermal oxidation works on the principle of an afterburner. The heat energy required to reach combustion temperatures is typically supplied by the oxidation of the contaminants in the more efficient systems. However, when only low concentrations of the contaminant are available, large amounts of energy must be added to the effluent stream to reach the required temperature to destroy the contaminants. In addition to creating thermal pollution and green house gases, it makes thermal oxidation inefficient and cost prohibitive.
Disposal of liquid and/or solid wastes containing these contaminants is also costly. It is desirable to treat hazardous contaminants using chemical reactions where the contaminant is converted to a non-hazardous or sometimes even useful reusable material. One specific example of this includes the decomposition of volatile organic halogenated compounds (VOHC) by passing the compound through a porous silica gel bed and exposing the gel to ultraviolet light and/or ozone. Some of the difficulties involved with this technology include the expense and difficulties of maintaining and regenerating the silica gel bed, particularly as the bed tends to foul when particulate matter is introduced in the stream to be treated. Another specific example of such reaction includes the destruction of perchlorethylene (PERC) in the dry cleaning industry by “burning up” the PERC using ozone. Both of the above methods require substantial amounts of ozone to achieve their goals. Furthermore, the use of ozone or other oxidizing agents for complete destruction requires the use of an amount stoichiometrically determined to completely convert the amount of contaminants available to H2O, CO2, and HCl. A very large amount of excess (i.e., beyond stoichiometric requirements) ozone or oxidizing agent is also consumed by other oxidizable materials present in the matrix. Even more ozone is catalytically converted back to O2 by reaction with itself, or wasted as an offgas to a destruction device that converts O3 back to O2. Ozone is undesirable as an off-gas. Additional steps become necessary to remove excess ozone. It is recognized that continued exposure to levels of ozone as low as 0.00010% are toxic. This can result in ozone or oxidant feed requirements that are 10 to 100 times the stoichiometric requirement.
Other available methods of removing contaminants from gases include liquid absorbent scrubbers. Liquid scrubbers contact the airborne contaminants with mist or fog that absorb or otherwise capture the contaminant in the gas or air stream and remove it from the stream. The air stream can then be safely vented to the atmosphere. All scrubbing liquids have a limit to the amount of contaminants they can absorb or carry. Once the scrubbing liquid's capacity has been reached, the liquid must be regenerated or discarded. Liquid scrubbers also frequently require expensive additives, such as metal chelates, defoamers, pH additives, reactive agents or other specialty chemicals. Scrubbing liquids are frequently selective to specific contaminants making them impractical for systems containing multiple contaminants.
Many industries have similar problems with treatment or disposal of contaminants from waste products. The-paint and coating industry is particularly plagued with problems due to the nature of the paints and coatings they use and produce. Many consumer and industrial items require coatings on the product. Such coatings are typically applied in a paint spray booth. A wide variety of coatings are in use today including latexes, lacquers, varnishes, enamels, epoxies, polyurethanes, catalyzed coatings, metal-containing paints, and many more. These coatings can be either oil based, solvent based, water based, solvent water emulsion based, or high solids catalyzed based (where the monomer acts as its own solvent for viscosity control). A paint spray booth is an enclosed ventilated area in which materials are sprayed or coated. As coating operations typically involve excess over-sprayed paint and-solvent vapors from the painting operation, the paint spray booth is intended to capture the over-spray while diluting the solvent vapors well below the lower explosive limit as they are collected and exhausted from the booth.
In water wash spray booths, forced air is used to direct the flow of over-spray to a water wash chamber. The over-spray particulate contaminants are trapped in the water wash scrubber section of the booth allowing the cleaned air to be vented or further processed. The water wash solution is typically fresh water with various chemicals added to defoam, detackify and flocculate the collected over-spray. One popular water wash booth solution is an oil-in-water emulsion. This emulsion solution is particularly effective at capturing a wide variety of paints in a paint spray booth. Various organic and synthetic oil systems are also used in liquid scrubbers but have not found favor in the paint booth scrubber application due to their cost and various recycling problems.
Peculiar to paint spray booths (as opposed to many other scrubber applications) is the issue that the paint hardens or becomes tacky and sticky as solvent evaporates from the previously captured paint particles. Paints that contact surfaces of the booth scrubber section create a film that grows thicker as deposits build up on the surface. Paint collected in air filters or in a wash section that is subjected to heat or drying becomes tacky. This causes, a problem in every aspect of paint booth operation, from the cleaning of equipment, walls and tanks to the further processing of removed sludge and solids. Water wash paint booths typically capture the particulate contaminants in a suitable liquid material (usually water) by contacting the liquid with the contaminants. Various chemicals are added to these liquids to provide detackifying properties. The addition of detackifying chemistry and flocculation chemistry increases the final sludge volume requiring disposal by up to 300–400%. These chemical additions are expensive in that they are costly to buy, require bath titrations and calculations to determine the correct amount and frequency of addition needed to maintain the booth, and increase the final disposal volume and cost by up to 400%. Since most industrial operations, including manufacturers, do some painting, the problems associated with painting operations are widespread.
The paint industry also produces paint sludge and substantial quantities of unused paint that must be discarded. Currently, sludge from existing water wash paint booths, and sludges from other industries that contain hazardous organic ingredients, solvents or metals, require very special and costly treatment. Separation of hazardous waste metals, water and organics from various waste streams that vary substantially from batch to batch make separation process scaleups nearly impossible to consider. Premium disposal rates are charge for organic sludges with heavy metal (hazardous) contamination that have low BTU value due to water content. There is a need for a method of converting high-concentration paint waste and sludge-like products with and without excess water content into useful or non-hazardous materials or by-products.
Manufactured items must first be cleaned in order to assure good adhesion of the paint to the item. Manufactured components must be cleaned of fabrication process surface contaminants such as fabrication oil, metal fines, shop dirt, dust and hand prints (oil). These contaminants are typically removed with a cleaning fluid. When the cleaning fluid becomes saturated with contaminants, it must either be reconditioned or discarded. Reconditioning typically includes separation of the contaminants from the fluids so that the fluids can be re-used. The contaminants are then merely in a concentrated form and still require disposal.
There is a need for a universal method and apparatus that addresses air pollution control and water pollution control such universal method being applicable to treat volatile contaminants produced by a variety of processes sources.
There is a need for a method and apparatus for converting hazardous, volatile and/or malodorous compounds into non-hazardous, less hazardous, non-volatile, less volatile, odorless and/or useful compounds.
There is a need for a method and an apparatus for cost-effective treatment of waste streams containing contaminants.
There is a need for a method of treating streams containing contaminants such that the contaminants are converted from hazardous to non-hazardous or less hazardous components.
There is a need for a method of oxidizing such contaminants involving substantially reduced amounts of oxidizing reagent.
There is a need for an air pollution control process and apparatus that can efficiently treat streams with low concentrations of contaminants.
There is a need for air pollution control processes that do not produce additional waste streams or waste products as a result of the pollution control process.
There is a need for a method and apparatus for the destruction or ultimate disposal of multiple and/or mixed environmental contaminants.
There is a need for a liquid-scrubbing process and apparatus that minimizes the cost of or need to regenerate the scrubbing liquid.
There is a need for a method and apparatus for detackifying scrubber liquids, sludges and the like.
There is a need for a method and apparatus for improving the filterability of scrubber liquids, sludges and the like.